1. Field of the Invention
The present invention relates to a vehicle travel control system which controls travel of a vehicle based on a travel plan.
2. Description of the Related Art
Technology to realize travel of a vehicle with low fuel consumption is disposed in Japanese Patent Application Publication No. 2007-187090 (JP-A-2007-187090). The vehicle travel control system is installed in a hybrid vehicle that an engine and a motor are drive sources. The system makes speed retaining control that a travel speed of the vehicle is retained at a target cruise speed. The vehicle travel control system sets an upper limit speed that is higher than the target cruise speed and a lower limit speed that is lower than the target cruise speed. The system makes the vehicle accelerate to the upper limit speed with the engine as the drive source, makes the vehicle travel with the engine being stopped when the speed reaches the upper limit speed, and starts the engine to make the vehicle accelerate when the speed reaches the lower limit speed.
However, there are cases that the non-stop state of the engine such as warm-up of the engine, battery, and heater occurs while the vehicle is traveling. In such a case, there is a possibility that the vehicle travel control system cannot realize the travel with low fuel consumption as planned and that the fuel efficiency deteriorates.